docs: def mark_log(self, filename='system.log'):
          """
          Returns "a mark" to the current position of this node Cassandra log.
          This is for use with the from_mark parameter of watch_log_for_* methods,
          allowing to watch the log from the position when this method was called.
          """
          log_file = os.path.join(self.get_path(), 'logs', filename)
          if not os.path.exists(log_file):
              return 0
          with open(log_file) as f:
              f.seek(0, os.SEEK_END)
              return f.tell()